Brake light wiring?
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Post Fiend
Joined: Jan 2003
Posts: 8,600
Likes: 4
From: Iowa
Brake light wiring?
Ok this is driving me nuts. Would someone please explain to me the complete wiring of the brake lights on a '70 F-100? I've replaced the light and that didn't work. I tried the old and new light in the other side and both worked fine. So I know the old, and new lights are OK. Yet, my left side brake light continues to be out. Please dont just tell me to go after it with a voltmeter, I know how to do that, but I need to know which wires to look for and where to look. A wiring diagram would be perfect, but if you just explain it to me that would be ok too.
Thanks!
Thanks!
Lead Driver
Joined: Jan 2003
Posts: 9,893
Likes: 12
From: Ohio
There are only FOUR wires to the back of the truck. The brown wire is running lights, the yellow and green ones are the left/right turn signal/brake wire and dont know what the back up light color is.
I take it you dont have turn signal back there either?? You shouldn't, they are both thru the same wire. If you DO have turn signal, the I would say it's the turn signal switch. Both brake lights run through this to make them function as both. If the turn signal functions only, then apparently the switch is faulty and not making contact for brake light operation.
Had a friend with this type of problem, only NOTHING worked out back. Here someone had torn the switch apart and got the contacts in backwards. Hence nothing worked at all. I put it back together properly and all was well. This was a 60's Chebby II, I dont think our switches come apart like this one did. But I see the similar problem.
Larry
I take it you dont have turn signal back there either?? You shouldn't, they are both thru the same wire. If you DO have turn signal, the I would say it's the turn signal switch. Both brake lights run through this to make them function as both. If the turn signal functions only, then apparently the switch is faulty and not making contact for brake light operation.
Had a friend with this type of problem, only NOTHING worked out back. Here someone had torn the switch apart and got the contacts in backwards. Hence nothing worked at all. I put it back together properly and all was well. This was a 60's Chebby II, I dont think our switches come apart like this one did. But I see the similar problem.
Larry
Senior User
Joined: Feb 2004
Posts: 325
Likes: 0
From: WEST TENN.
Hey,
I am going thru the same thing, replaced lights, brake light switch, but it only works when either 4 ways, or turn signal is working, guy told me same thing happened on his 86 model, so tomarrow I am pulling the switch, I will let you know what I find.
I am going thru the same thing, replaced lights, brake light switch, but it only works when either 4 ways, or turn signal is working, guy told me same thing happened on his 86 model, so tomarrow I am pulling the switch, I will let you know what I find.
Lead Driver
Joined: Jan 2003
Posts: 9,893
Likes: 12
From: Ohio
Yes the brake lights and turn signals are the same bulb, so they have to go thru the turn signal switch to be able to be used as both. Two sets of contacts, when in center the brake switch current is sent to both bulbs to activate as brake lights. When you operate the turn signals, it divides it up so one acts as brake the other as turn. Simple, but complex.
You will need a steering wheel puller(at any parts store). Remove horn hub, remove large nut. Install puller and remove wheel. Unscrew turn signal stalk and unbolt switch. You will need to unplug wires at bottom of column. You will have to also remove wires from plug, as plug will not fit up thru column. Take a piece of paper and layout the plug and which wires go where. It takes some finesse to get wire tags out of plug, but it happens. Pull wires up thru column and reverse for new switch. Slip the wheel back on and tighten the nut.
Sounds complicated, but it's relatively simple procedure.
Larry
You will need a steering wheel puller(at any parts store). Remove horn hub, remove large nut. Install puller and remove wheel. Unscrew turn signal stalk and unbolt switch. You will need to unplug wires at bottom of column. You will have to also remove wires from plug, as plug will not fit up thru column. Take a piece of paper and layout the plug and which wires go where. It takes some finesse to get wire tags out of plug, but it happens. Pull wires up thru column and reverse for new switch. Slip the wheel back on and tighten the nut.
Sounds complicated, but it's relatively simple procedure.
Larry
Trending Topics
Senior User
Joined: Feb 2004
Posts: 325
Likes: 0
From: WEST TENN.
Update,
TURN SIGNAL SWITCH
I changed mine from my parts truck to my good truck, now I have brake lights!! whoohoo
TURN SIGNAL SWITCH
I changed mine from my parts truck to my good truck, now I have brake lights!! whoohoo
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Tuned
Joined: Jul 2003
Posts: 374
Likes: 0
From: Dudley, GA
Other problems can in the wiring itself. It runs down the drivers side frame rail, inspect all of it and make sure there are no kinks or exposed wires. I was blowing fuses left and right, found the whole wire bundle pinched under the trans cross member. Who ever did that work should have been slapped (wasn't me)!
Post Fiend
Joined: Jun 2002
Posts: 13,873
Likes: 3
From: Atlanta GA
Make a 15-20 foot lead with alligator clips. Red wire if possible, with a 15 amp fuse. Put a spdt switch inline and make sure it is wrapped nicely so it does not short out.
Unplug the 4 connector harness to the rear lights under the hood on the drivers side. Take your clip, one end on the (+) battery, place it on a connector, hit the switch and make sure the lamp lights.
Then, take a test lamp, shove it into a L/R connector from the truck side, press the brakes and see if it lights. If it does not, you know the problem is inside the cab for sure.
As this point where one side works and the other does not, I would replace the turn signal switch, as someone mentioned.
Unplug the 4 connector harness to the rear lights under the hood on the drivers side. Take your clip, one end on the (+) battery, place it on a connector, hit the switch and make sure the lamp lights.
Then, take a test lamp, shove it into a L/R connector from the truck side, press the brakes and see if it lights. If it does not, you know the problem is inside the cab for sure.
As this point where one side works and the other does not, I would replace the turn signal switch, as someone mentioned.
Junior User
Joined: Dec 2003
Posts: 70
Likes: 0
From: Spokane, WA
Hey Frieghtrain,
Isn't this very switch attached to the back of the instrument panel? (I've only got my '69 to refer to), but it didn't seem to me like I had to pull the wheel to fix mine...just a lot of stuffing of my hands up in there...
J
Isn't this very switch attached to the back of the instrument panel? (I've only got my '69 to refer to), but it didn't seem to me like I had to pull the wheel to fix mine...just a lot of stuffing of my hands up in there...
J